If you really need a Shulchan Aruch which addresses this type of issue, I'll quote from the end of hilchos yom tov siman 529 where the Mechaber just finished talking about simchas yom tov and what bad things can come out from too much fun. He then brings from the Rambam:
"Beis Din is required to appoint watchmen on the festivals to go wandering and searching in the gardens and orchards and rivers so that men and women won't gather there to eat and drink which can bring to Aveira. And also warn all the people not to mingle men and women in their houses in happiness, and not be drawn after wine so as not to come to Aveira, but rather all should be holy".
The Mishna Berurah points out that the truth is this is required at all times and whoever has the ability to stop people should, but during the holidays these acts are more common.
The Aruch Hashulchan in siman 583 siff 4 says men and women should not be going to Tashlich together, and if a certain place has women going there, men should rather not go at all.
There is also a Torah Temimah on Esher 1 9 גם ושתי עשתה משתה נשים בית המלכות אשר למלך אחשורוש. He brings the gemara in Megila 12a that darshans we see that she also had bad intentions because it didn't say beis hanashim. Torah Temimah explains that Beis nashim would have meant the women sitting separate from the men, as it is it means they were also in the Beis Malchus, men and women mixed.